The present invention relates to a system for ultrasonically exciting the a piezoelectric crystal used in an ultrasonic ranging device.
In North America and throughout the world, there are substantial numbers of propane fuel tanks installed outside residential and commercial premises to provide energy for heating, cooling and cooking. These tanks can range in size from ones which have a relatively small capacity (e.g. 50 gallons) to ones which have a relatively large capacity (e.g. 1000 gallons or more). Often, the propane fuel is sold by a propane distributor to its customers under a contract where the distributor provides the customer with the tank in return for the exclusive right to supply the customer with the fuel.
Accordingly, there is a need in the propane industry for a direct method of monitoring customer inventory. In this respect, there are existing fuel tank mounted mechanical gauges which can be installed to provide an approximate indication of inventory. However, the readings they provide are typically quite unreliable (e.g. an error range of plus or minus 10% to 20%). An option that would provide improved accuracy would be to install on each tank a totalizing flow meter like that used by a fuel truck when delivering fuel to a tank, or comparable to that used by utilities that supply electricity, natural gas or water to utility customers. Then, the total volume of fuel removed from the tank then could be recorded and regularly compared with the volume when the tank was filled. However, apart from the cost of installing and maintaining such precision flow meters, the customers of a propane distributor are often located in non-urban areas. The distance between such customers can be too large to justify the repetitive manual collection of usage data.
It is known to sense the level of liquid contained in a tank utilizing sonic measurement techniques; typically sonic or ultrasonic measurements made with the use of a piezoelectric crystal. If the level of liquid is known and the geometry of the tank is known, then the volume of liquid in the tank can be calculated based upon the measured level. However, when the liquid in question is propane and the tank in question is a propane tank, problems arise. One problem is the adequacy of acoustic coupling between the ultrasonic transducer and the fuel tank. If the coupling is poor, then it may not be possible to obtain a measurement, or any measurement made may be unreliable. Another problem is the voltage levels which are generated by the transducer. If relatively high voltages are involved, then regulatory approval may be difficult or impossible to obtain. Dominating any solution to such problems is the question of cost. A solution which enables direct measurement but which requires a costly installation on each fuel tank of each customer is an impractical solution.